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The close-mid back protruded vowel is the most common variant of the close-mid back rounded vowel. It is typically transcribed in IPA simply as ⟨o⟩, and that is the convention used in this article. As there is no dedicated diacritic for protrusion in the IPA, the symbol for the close-mid back rounded vowel with an old diacritic for labialization, ⟨ ̫⟩, can be used as an ad hoc symbol ⟨o̫⟩ for the close-mid back protruded vowel. Another possible transcription is ⟨oʷ⟩ or ⟨ɤʷ⟩ (a close-mid back vowel modified by endolabialization), but this could be misread as a diphthong.

For the close-mid near-back protruded vowel that is usually transcribed with the symbol ⟨ʊ⟩, see near-close back protruded vowel. If the usual symbol is ⟨o⟩, the vowel is listed here.

Its vowel backness is back, which means the tongue is positioned as far back as possible in the mouth without creating a constriction that would be classified as a consonant. Unrounded back vowels tend to be centralized, which means that often they are in fact near-back.

Its roundedness is protruded, which means that the corners of the lips are drawn together, and the inner surfaces exposed.

Realization of /ɔː/ reported to occur in dialects spoken near the river Ipeľ, as well as - under Hungarian influence - in some other speakers. Corresponds to mid [ɔ̝ː] in standard Slovak.[47] See Slovak phonology

There is no dedicated diacritic for compression in the IPA. However, compression of the lips can be shown with ⟨β̞⟩ as ⟨ɤ͡β̞⟩ (simultaneous [ɤ] and labial compression) or ⟨ɤᵝ⟩ ([ɤ] modified with labial compression). The spread-lip diacritic ⟨ ͍ ⟩ may also be used with a rounded vowel letter ⟨o͍⟩ as an ad hoc symbol, but 'spread' technically means unrounded.

Only Shanghainese is known to contrast it with the more typical protruded (endolabial) close-mid back vowel, but the height of both vowels varies from close to close-mid.[6]

Its vowel backness is back, which means the tongue is positioned as far back as possible in the mouth without creating a constriction that would be classified as a consonant. Unrounded back vowels tend to be centralized, which means that often they are in fact near-back.

Its roundedness is compressed, which means that the margins of the lips are tense and drawn together in such a way that the inner surfaces are not exposed.

Dankovičová, Jana (1999), "Czech", Handbook of the International Phonetic Association: A guide to the use of the International Phonetic Alphabet, Cambridge: Cambridge University Press, pp. 70–74, ISBN0-521-65236-7

Deterding, David (2000), "Measurements of the /eɪ/ and /oʊ/ vowels of young English speakers in Singapore", in Brown, Adam; Deterding, David; Ling, Low Ee Ling, The English Language in Singapore: Research on Pronunciation, Singapore: Singapore Association for Applied Linguistics, pp. 93–99

Engstrand, Olle (1999), "Swedish", Handbook of the International Phonetic Association: A Guide to the usage of the International Phonetic Alphabet., Cambridge: Cambridge University Press, pp. 140–142, ISBN0-521-63751-1